One of the most elegant and tightly regulated mechanisms for gene expression is alternative pre-mRNA splicing. Despite the undisputed importance of regulated splicing in several developmental processes and human disease, relatively little is known about the mechanisms by which specific alternative splice choices are regulated. Importantly, the identification of numerous alternatively spliced isoforms in cancer highlights the potential role of the spliceome in the tumor phenotype. Recently, we have shown that specific types of cell stress initiate coordinated alternative splicing of the p53 modulators mdm2 and mdm4 (mdmx). The predominant activity of the mdm2 alternative transcripts is to activate the p53 pathway by inhibiting MDM2 in a dominant negative fashion. These same alternative transcripts have been identified in numerous human tumors. We are interested in studying the regulation of mdm2 splicing to gain a better understanding of 1) regulation of the p53 pathway by alternative splicing in cancer 2) the relationship between the cancer spliceome and the cancer phenotype and 3) the role of the resultant spliced forms in the induction of cancer. Our data suggest that some transformed cells provide a constant signal to activate p53 through sustained expression of mdm2 alternatively spliced transcripts. The proposed research will elucidate the molecular connection between RNA splicing, the p53 response, and ultimately cancer. Unraveling this pathway will undoubtedly lead to the discovery of novel therapeutic intervention points and thus be a crucial stepping-stone for drug discovery.